Installations are known which include portable, wireless telephones and which include one or more stationary units connected to a telephone network, the portable telephones being in radio communication with these stationary units. In the installation, there are one or more pairs of portable telephone and stationary units, the rage of radio communication being limited, for example, to an apartment or house. An installation built in this way is well suited for use in dwellings, both in single-family houses and in large apartment houses. Installations of this kind are described in SE-B-8107663-0.
Adaptive channel selection is described in this publication. In each of the units, there is selected from a radio speech channel which is idle and is selected among a plurality of radio speech channels, common to all pairs. It will thus be unnecessary to plan assigning of frequencies to the wireless telephone sets.
Even earlier mobile telephone systems are known in which mobile telephones, often in automobiles, can be put into radio communication with one of a plurality of fixed radio stations. Such type of fixed station transmits on a plurality of assigned radio frequencies, adjacent fixed stations being assigned other frequencies so that disturbance or noise is avoided. Should a corresponding principle for frequency assigning be used for the portable, wireless telephones as intended in the present invention, the administration of the frequency assignment would be extremely cumbersome and the frequency economy poor.
In a large office block, the concentration of portable telephones tends to be severe, and there may be the demand that a user of a portable telephone must carry the telephone with him within the entire office block. The relation between portable telephone and stationary unit will be looser than in the case described earlier. A given stationary unit can not service a portable telephone everywhere in the large block since the transmitting power of both telephone set and stationary unit must be kept down in consideration of noise.